The normal movements of the human ankle during activities such as walking, running and various types of athletics are, as illustrated in FIG. 8, dorsiflexion D and plantar flexion P, both of which occur in a sagittal plane. For such activities it is important that these types of flexion not be unduly restricted.
Conversely, the ankle is not normally intended to move abruptly or excessively in inversion I or eversion E as illustrated in FIG. 7. While a person does make slight inversion and eversion movements of the ankle in walking and athletics, external forces to which the ankle is subject can cause undue, excessive or abrupt inversion or eversion torque which results in serious ankle injury. For instance, during sports an athlete can step or land heavily on the side of his or her foot, or a walker can accidentally step off the side of a curb or have his or her ankle turned by stepping on an irregular patch of ground or sidewalk.
In addition to such type of ankle injuries, ankle motion frequently needs to be controlled after surgical procedures. It is common for those recovering from foot, ankle or leg surgery to go through several phases of protective devices following the surgery until the foot, ankle or leg is completely healed and rehabilitated. The early phases often involve complete immobilization of the ankle while later phases involve less restrictions on movement. Throughout all the phases, however, good recovery normally requires that excessive inversion and eversion be completely avoided. It is also not uncommon for a physician to recommend that even after healing and rehabilitation the patient take precautions against incurring abrupt or excessive inversion or eversion.
Over the years there have been many approaches to preventing injurious inversion and eversion ankle motions. Most have involved means of immobilizing the ankle to various degrees. One common technique widely used in sports is to provide a tight tape binding around the ankle and longitudinal arch of the foot. This is of somewhat limited effectiveness, however, for the tape cannot be so tight as to restrict the athlete from running, jumping or performing similar motions required by the sport, and therefore the tape is of little effectiveness against the more severe forces that cause injury. Further, tape cannot be left in position for more than a few hours, is relatively uncomfortable to the athlete and is difficult to apply properly (often requiring the assistance of another person such as a sports trainer).
Numerous mechanical devices, commonly known as ankle-foot orthoses ("AFO's") have been developed to deal with plantar flexion and dorsiflexion problems. Such problems may arise from illnesses, such as polio, and prevent a person from being able to control flexion of the ankle (commonly called "drop foot"), or may result from ankle injuries. These AFO's can be grouped into two categories: those which are analogous to tape wrapping systems, usually having a preformed type of wrapping, and those which use mechanical leg braces. The latter are more pertinent to the present invention. Many patents illustrate examples of these types.
A good description of representative examples of the leg brace type is found in the Atlas of Orthotics (2d edn.; 1985), published by the American Academy of Orthopaedic Surgeons, in chapter 10, "Lower-Limb Orthoses" by S. Fishman et al. These can be considered to have a "parallelogram" structure if viewed from the anterior or posterior direction, as illustrated in FIG. 10B. AFO's are designed solely to limit, assist or restrict plantar flexion and/or dorsiflexion. They do not effectively deal with inversion and eversion, nor are they designed to do so.
In addition, AFO's suffer from a variety of disadvantages:
1. The leg braces are rigid and any flexural motion of the foot comes only through the use of complicated hinge mechanisms. These hinge mechanisms in turn must usually have complex built-in stops to prevent excessive flexion. Other accommodation to the rigidity is obtained through added structures of resilient padding or springs to allow motion.
2. The rigidity of the braces can cause abrasion of the calf muscles as the user walks.
3. The rigidity limits the use of the AFO's so that they cannot be effectively worn for sports or other activities in which running, jumping and similar leg, ankle and foot movements are necessary.
4. The leg brace AFO's generally require the use of a sturdy shoe to be effective. Even those which involve shoe inserts still require a wide shoe with little flexibility to accommodate the metal braces and hinge mechanisms. This effectively precludes the use of AFO's in soft shoes such as athletic shoes.
5. Virtually all AFO's must be custom fitted to the individual user, to accommodate the user's feet and legs.
6. The AFO's are unsightly, and because of their spread configuration they are difficult to conceal under trousers.
7. Because of their spread configuration and lateral orientation to the leg, they are also hazardous to other individuals with whom the user may come into physical contact. For example, if an athlete were to use a leg brace AFO during a contact sporting event such as basketball (notwithstanding the rigidity problems), other players would be at risk of receiving lacerations, bruises or other injuries to their lower legs by hitting the braces during play.
Other types of AFO's act through a single brace aligned posterior to the lower leg and in the same sagittal plane. Typically these AFO's attach to the heel of a shoe. They have no ability to resist inversion or eversion torque since they are aligned along the center line of the ankle and foot and therefore have no resistive moment arm. The shoe cannot serve to transfer lateral forces to the central brace since it is not sufficiently rigid.
It would therefore be advantageous to have an ankle orthosis which could be readily accommodated to the posterior portion of a user's lower leg and which would effectively transfer torque-producing forces from the foot to the tibia to prevent eversion an inversion but still retain substantially free dorsiflexion and plantar flexion. Such a device should be usable in medical and therapeutic applications, as postoperative uses. It should also be useful as a prophylactic device, such that it could be used by athletes in active sports to reduce or eliminate the need for prior practices such as taping. It would also be advantageous if the device were capable of being conveniently and comfortably used by anyone who wishes to prevent ankle injuries incurred during ordinary daily activities such as walking, climbing stairs, etc. Further, the device should be capable of being manufactured in a limited number of widely applicable sizes so that it can be readily used by anyone without having to go through tedious and expensive custom fitting of the device to each user.